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| United States Patent |
6,024,028
|
|
Simonen
|
February 15, 2000
|
Protection of the air ports of a recovery boiler
Abstract
A method and apparatus for extending the life of air ports and nozzles in
furnaces, particularly recovery boilers for burning black liquor to
produce heat and a chemical melt. Apparatus is provided for feeding
combustion air into a furnace having a tube wall, the apparatus
comprising: an air port disposed in the tube wall, and connected to an air
duct through which air flows into and then through the air port, and into
the furnace; and a protective insert of heat conductive and heat and
corrosion resistant material mounted in the air port and positioned so
that it is cooled by the air flowing through the air port. The protective
insert has sufficient thermal mass (e.g. a volume of between
40,000-4,000,000 cubic mm) so as to effectively even out temperature peaks
caused by melt splashes from the furnace impacting the vicinity of the air
port, e. g. the protective insert is made out of highly corrosion
resistant steel such as stainless steel. The air port may be defined by,
or comprise, a nozzle having an interior and a bottom portion; and wherein
the protective insert is preferably releasably mounted to the interior
bottom portion of the nozzle in the air flow from an air duct to the
furnace.
| Inventors:
|
Simonen; Jorma (Marietta, GA)
|
| Assignee:
|
Ahlstrom Machinery Oy (Helsinki, FI)
|
| Appl. No.:
|
038059 |
| Filed:
|
March 11, 1998 |
| Current U.S. Class: |
110/182.5; 110/238; 110/343; 122/6.6; 239/591 |
| Intern'l Class: |
F23L 005/00 |
| Field of Search: |
239/591
110/182.5,297,309,310,313,343,349,238
122/6.5,6.6
|
References Cited
U.S. Patent Documents
| 1862341 | Jun., 1932 | Holzworth | 122/6.
|
| 3015481 | Jan., 1962 | Clingensmith | 122/6.
|
| 3188070 | Jun., 1965 | Lee | 110/182.
|
| 3545736 | Dec., 1970 | Zimmermann | 122/6.
|
| 3589318 | Jun., 1971 | Szatkowski | 110/182.
|
| 3831857 | Aug., 1974 | Scott | 239/591.
|
| 3845729 | Nov., 1974 | Von Berlichingen | 110/182.
|
| 4759297 | Jul., 1988 | McNally et al. | 110/182.
|
| 5528999 | Jun., 1996 | Salmi | 110/182.
|
| Foreign Patent Documents |
| 54-124312 | Sep., 1979 | JP | 239/591.
|
| 8-188977 | Aug., 1996 | JP.
| |
| 351 029 | Jan., 1972 | SE.
| |
Primary Examiner: Lazarus; Ira S.
Assistant Examiner: Ciric; Ljiljana V.
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority of Provisional 60/039,605 filed Mar.
12, 1997.
Claims
What is claimed is:
1. Apparatus for feeding combustion air into a furnace having a tube wall,
said apparatus comprising:
an air port disposed in said tube wall, and connected to an air duct
through which air flows into and then through the air port, and into said
furnace; and
a protective insert of heat resistant and corrosion resistant material
mounted in said air port and positioned so that said protective insert is
cooled by the air flowing through said air port, said protective insert
has sufficient thermal mass so as to effectively even out temperature
peaks caused by melt splashes from the furnace impacting the vicinity of
said air port.
2. Apparatus as recited in claim 1 wherein said protective insert is made
out of highly corrosion resistant steel.
3. Apparatus as recited in claim 2 wherein said protective insert has a
volume of between about 40,000-4,000,000 cubic mm.
4. Apparatus as recited in claim 1 wherein said air port is defined by a
nozzle having an interior bottom portion; and wherein said protective
insert is mounted to said interior bottom portion of said nozzle.
5. Apparatus as recited in claim 4 wherein said insert is mounted by a
connection to said air port so that said insert can be easily replaced.
6. Apparatus as recited in claim 4 wherein said insert is not in contact
with said tube walls.
7. Apparatus as recited in claim 4 further comprising a refractory-filled
box and positioned attached to said tube wall, said air port disposed
within said box adjacent said tube wall.
8. Apparatus as recited in claim 7 wherein said insert extends within said
nozzle, away from said tube wall, a linear distance from said box of about
100-700 mm.
9. Apparatus as recited in claim 8 wherein said insert has a maximum height
of to about 20-50 mm when said air port has a height of about 150-200 mm.
10. Apparatus as recited in claim 8 wherein said insert tapers so that said
insert has a smaller cross-sectional area more remote from said box than
adjacent said box, and wherein the largest cross-sectional area of said
insert is about 10-50% of the cross-sectional area of said air port
without said insert.
11. Apparatus as recited in claim 4 wherein said insert has an upper
surface, said upper surface most remote from said interior bottom portion;
and wherein said upper surface is convexly curved.
12. Apparatus as recited in claim 1 wherein said insert is of stainless
steel or acid proof steel.
13. Apparatus as recited in claim 1 further comprising a refractory-filled
box and positioned attached to said tube wall, said air port disposed
within said box adjacent said tube wall.
14. Apparatus as recited in claim 1 wherein said air port further comprises
a nozzle extending into said air duct, said nozzle having an interior and
bottom portion; and wherein said protective insert is mounted to said
interior bottom portion of said nozzle, and extends within said nozzle a
distance of between about 150-500 mm.
15. Apparatus as recited in claim 14 wherein the largest cross-sectional
area of said insert is about 10-50% of the cross-sectional area of said
air port without said insert.
16. Apparatus as recited in claim 14 wherein said insert has a height which
tapers so that said insert has a smaller cross-sectional area more remote
from said tube wall than closer to said tube wall.
17. Apparatus as recited in claim 14 wherein said insert has an upper
surface, said upper surface most remote from said interior bottom portion;
and wherein said upper surface is convexly curved.
18. A recovery boiler for burning black liquor of a pulp and paper mill to
produce heat and to recover chemicals from the black liquor, said recovery
boiler comprising:
a furnace having a tube wall, and a black liquor inlet;
an air port disposed in said tube wall, and connected to an air duct
through which air flows into and then through the air port, and into said
furnace;
a protective insert of heat resistant and corrosion resistant heat
conductive material mounted in said air port and positioned so that said
insert is cooled by the air flowing through said air port; and
wherein said protective insert has sufficient thermal mass so as to
effectively even out temperature peaks caused by melt splashes as a result
of black liquor burning in said furnace and impacting the vicinity of said
air port.
19. A recovery boiler as recited in claim 18 wherein said protective insert
is made out of highly corrosion resistant steel and has a volume between
40,000-4,000,000 cubic millimeters.
20. A recovery boiler as recited in claim 18 wherein said air port further
comprises nozzle extending into said air duct, said nozzle having an
interior and a bottom portion; and wherein said protective insert is
mounted to said interior bottom portion of said nozzle, and extends within
said nozzle a distance of between about 150-500 mm.
21. A recovery boiler as recited in claim 20 further comprising a
refractory filled box and positioned attached to said tube wall, said air
port disposed within said box adjacent said tube wall; and wherein said
insert tapers so that said insert has a smaller cross-sectional area more
remote from said box than adjacent said box; and wherein the largest
cross-sectional area of said insert is about 10-50% of the cross-sectional
area of said air port without said insert.
22. Apparatus for feeding combustion air into a furnace having a tube wall,
said apparatus comprising:
an air port disposed in said tube wall, and connected to an air duct
through which air flows into and then through the air port, and into said
furnace;
a protective insert of heat and corrosion resistant material mounted in
said air port and positioned so that said insert is cooled by the air
flowing through said air port;
wherein said air port further comprises a nozzle extending into said air
duct, said nozzle having an interior bottom portion and an interior top
portion; and
wherein said protective insert is mounted to said interior bottom portion
of said nozzle and spaced from said interior top portion, and extends
within said nozzle a distance of between about 150-500 mm.
23. Apparatus as recited in claim 22 wherein the largest cross-sectional
area of said insert is about 10-50% of the cross-sectional area of said
air port without said insert.
24. Apparatus as recited in claim 22 wherein said insert has a height which
tapers so that said insert has a smaller cross-sectional area more remote
from said tube wall than closer to said tube wall.
25. Apparatus as recited in claim 22 wherein said insert has an upper
surface, most remote from said interior bottom portion; and wherein said
upper surface is convexly curved.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an apparatus for leading combustion air to
a furnace, which apparatus comprises an air port disposed in the furnace.
The air port is connected to an air distribution channel positioned
outside the tube wall of the furnace, from which the air flows through the
air port into the furnace.
Black liquor obtained from the production of chemical pulp is burnt in a
recovery boiler. The air required for the combustion of the organic
material in the black liquor is fed to the furnace of the boiler from air
distribution channels disposed at various levels around the furnace,
through the air ports in the wall of the furnace. Usually nozzles are
disposed in the openings in the wall so as to direct air into the furnace.
The air is most commonly introduced into the furnace at three levels. At
the lowest level is the primary air level, above this, is a secondary air
level, and the highest level, above the liquor nozzles, is the tertiary
air level. There may also be more than three air levels in the boiler.
Air nozzles have been manufactured of different types of steel and are
typically welded or fully cast. Nozzles manufactured of different
refractory materials are also used. There are basically two structures
that may be used in air nozzles. In one of these structures a nozzle is
attached to a gas-tight air port opening formed by bending wall tubes, by
for example welding a nozzle made of metal plates into the sides of said
tubes. The nozzles may also be attached onto the tube panels by a screw
joint. The nozzles are conventionally located inside a box filled with
refractory material, the outer shell of which is a steel plate. The boxes
are connected to the tube walls, and are usually filled with refractory
material. The refractory material protects the nozzle structures and
causes heat to move out of the nozzle.
In another embodiment, the nozzle is a distinct structure, and does not
form a gas-tight or melt-tight structure with the wall of the boiler. This
is a distinct disadvantage of this embodiment.
The combustion air is directed into the nozzles from air ducts encircling
(surrounding) the boiler. The air ducts usually include air controlling
devices for each of nozzles. The air passes through an air guide, and then
an air nozzle, into the furnace.
Conventional air nozzles have a tendency to corrode and crack, and
therefore require continuous maintenance in recovery boilers (soda and
other types of boilers) burning waste liquors (e.g. black liquor) from the
forest industry. This is especially true for the primary air nozzles in a
recovery boiler. While the maintenance of the nozzles itself is expensive,
a much more significant reason why the corrosion and cracking is dangerous
is that nozzle damage may creep into the adjacent water-cooled tubes on
the walls of the furnace of the boiler. A water leak in these tubes may
cause a melt explosion in the boiler, with potentially disastrous
consequences.
One significant reason for the above-mentioned corrosion and cracking of
the nozzles and their surroundings is the splashing of the melt generated
in the furnace into the air ports, especially into the primary air ports
(which are located at the lowest level). The main components of the melt
in a sulphate process are sodium carbonate and sodium sulphide. The melt
splashes, which have a volume of at least several liters, cause rapid
heating of the structure of the air port up to the melting point of the
melt, so that the melt salts cause corrosion and erosion in the air ports.
Rapid changes in the nozzle temperature also generate thermal fatigue and
stress corrosion in the structures of the air port and even in the
surrounding tubes of the furnace. Studies have shown that the temperature
of the primary air nozzle, when not properly cooled, varies very rapidly.
For example, during the first two hours of a four-hour test period, the
temperature varied substantially constantly between about 500 and
850.degree. C. For the last two hours, the temperature dropped so that it
was between about 350 and 500.degree. C. most of the time, rising
occasionally up to about 600.degree. C. The temperature peaks indicate
splashing of melt into the air nozzle.
The air ports and structures in the vicinity thereof are typically cooled
by the combustion air being fed to the furnace. They get rapidly damaged
if the feed of the combustion air from the port in question is interrupted
by closing its respective air damper.
Repairs of air nozzles have to be done regularly during shutdowns. The
repairs are difficult and laborious to effect. Dismantling of equipment is
necessary and the removal of old nozzles is difficult and time-consuming.
Therefore, the shutdowns often last a long time, causing losses in
production.
According to the present invention is possible to provide an apparatus for
feeding combustion air into the furnace in which the air ports and the
structures of the wall of the furnace in the vicinity thereof are
protected better than in the prior art against the effects of corrosion
and temperature changes. The invention protects the air ports of a boiler
burning waste liquor from pulp and paper industries (e.g. black liquor),
for example the ports of a recovery boiler, from corrosion and cracking.
The invention is especially useful in protecting the primary air ports
closest to the melt bed, which are exposed to detrimental effects of the
melt. In addition, the invention provides an apparatus that is easy to
maintain and repair, so that it is possible to decrease repair and
shutdown costs significantly.
According to the present invention the lower part of the air port is
provided with a protective insert which is made of substantially
heat-and-corrosion-resistant material and mounted and positioned in such a
way that it is cooled by the air flowing through the port. That is, the
apparatus according to the invention is provided with a separate thermal
mass protective insert, so that temperature peaks caused by melt splashes
can be effectively evened out, and the structures of the port (especially
those at the bottom) can be effectively protected against corrosion and
cracking. The protective insert is made of substantially
corrosion-resistant material, for example of stainless steel or acid-proof
steel. The elongated protective insert according to the invention is
attached in such a way that it can be detached relatively easily and may
be changed, when needed. The protective insert is also attached in such a
way that changing it does not damage the point of attachment or the
surroundings thereof. Typically, the insert is disposed at the lower part
of the nozzle of the air port, so that it is not in contact with the wall
tubes and so that the insert does not have to be detached from the wall
tubes of the boiler when the insert is replaced.
The protective insert according to the invention is attached, for example
by welding it lightly into the air port, in such a way that the
temperature peaks do not cause cracking or corrosion of the cooling tubes
of the furnace. Using the massive protective insert cooled by combustion
air, cooling capacity may be stored up and then used to cool the structure
when melt splashes occur. The protective inserts protect the air ports
against the immediate attack of melt and, due to their heat capacity, cool
a melt splash so that the temperature rise from a melt splash does not
affect the structures surrounding the protective insert.
According to one aspect of the present invention, there is provided an
apparatus for feeding combustion air into a furnace having a tube wall.
The apparatus comprises: An air port disposed in the tube wall, and
connected to an air duct through which air flows into and then through the
air port, and into the furnace; and a protective insert of heat and
corrosion resistant material mounted in the air port and positioned so
that it is cooled by the air flowing through the air port. Preferably the
protective insert has sufficient thermal mass so as to effectively even
out temperature peaks caused by melt splashes from the furnace impacting
the vicinity of the air port. For example, the protective insert is made
out of highly corrosion resistant steel (such as stainless steel, or acid
proof steel), or a like corrosion resistant high thermal conductivity
material, and has a volume of between about 40,000-4,000,000 cubic mm
(e.g. between about 1-2 million cubic mm).
The air port may be defined by (or the air port further comprises) a nozzle
extending into the air duct the nozzle having an interior and a bottom
portion; and the protective insert is preferably mounted to the interior
bottom portion of the nozzle, and so that it can be easily replaced. The
insert is not in contact with the tube walls.
The apparatus preferably further comprises a refractory filled box attached
to the tube wall, the air port disposed within the box adjacent the tube
wall.
Also, the insert preferably has an upper surface, most remote from the
interior bottom portion; and the upper surface is either flat, or
preferably convexly curved. The insert extends within the nozzle, away
from the tube wall, a linear distance from the box about 100-700 mm,
preferably about 150-500 mm. Also, the insert preferably has a height
proportional to about 20-50 mm when the air port has a height of about
150-200 mm, and the insert tapers so that it has a smaller cross-sectional
area more remote from the box than adjacent the box; that is the insert
has a height which tapers so that it has a smaller cross-sectional area
more remote from the tube wall than closer the tube wall. The largest
cross-sectional area of the insert is typically about 10-50%, preferably
about 15-30%, of the cross-sectional area of the air port within the
insert.
According to another aspect of the invention, there is provided a recovery
boiler for burning black liquor of a pulp and paper mill to produce heat
and to recover chemicals therefrom. The recovery boiler comprises: A
furnace having a tube wall, and a black liquor inlet. An air port disposed
in the tube wall, and connected to an air duct through which air flows
into and then through the air port, and into the furnace. A protective
insert of heat and corrosion resistant heat conductive material mounted in
the air port and positioned so that it is cooled by the air flowing
through the air port; and wherein the protective insert has sufficient
thermal mass so as to effectively even out temperature peaks caused by
melt splashes as a result of black liquor burning in the furnace and
impacting the vicinity of the air port.
According to yet another aspect of the invention there is provided a method
of recovering heat and chemicals from black liquor produced by the
chemical pulping of cellulose, utilizing a recovery boiler having a
furnace with a tube wall, and air ports at least some of which contain
nozzles leading from the air ports into an air duct, each nozzle having a
bottom interior portion. The method comprises the steps of: (a) Causing
air to flow from the air duct, through the nozzles and air ports into the
furnace to provide combustion air. (b) Feeding black liquor into the
furnace to combust with the combustion air to produce heat energy and
produce a melt. (c) Mounting protective inserts of heat conductive
corrosion resistant material in at least some of the nozzles on the bottom
interior portions thereof, the inserts having sufficient thermal mass so
that when cooled by air flowing through the nozzles they even out the
temperature peaks caused by melt splashing onto structures in the vicinity
of the air ports, and thereby increase the life of the air ports and
nozzles; and (d) withdrawing melt from the furnace for chemical recovery.
Step (c) is preferably practiced by readily releasably mounting the
inserts in the nozzles, distinct from the tube wall; and the method
comprises the further step of replacing the inserts when worn without
disturbing the tube wall or having to replace the nozzles.
It is the primary object of the present invention to provide enhanced
longevity for air ports and/or nozzles in recovery boilers, or the like.
This and other objects will be clear from the detailed description and
from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates the lower part of a furnace in a recovery
boiler;
FIG. 2 schematically illustrates an embodiment according to the invention
in which the air port and the protective insert disposed therein are shown
in cross-section; and
FIG. 3 illustrates the embodiment according to FIG. 2 seen from the inside
of the furnace along line A--A.
DETAILED DESCRIPTION OF THE DRAWINGS
The lower part of a furnace 2 of a recovery boiler according to the
invention comprises a bottom 3 and walls 4 of the boiler. Black liquor is
fed into the furnace, so that in the combustion process, a bed 6 is formed
of dried and partly burnt liquor at the bottom of the boiler. The molten
chemicals flow through the porous bed to the bottom of the furnace, and
then they are passed as an overflow through melt chutes into the dissolver
7. Air is fed to the bottom of the furnace from two different levels:
through primary air ports 9 and secondary air ports 10 from the air ducts
5 surrounding the boiler. At an upper level of the furnace 2 there are one
or more other air levels. The feeding of air, and air feeding apparatus
used for that purpose (for example air ducts), may utilize any
conventional air controlling devices and air port cleaners.
The walls of the furnace 2 are constructed of water cooled tubes 11
connected to a conventional superheater and steam generating parts (not
shown) of the recovery boiler. The required number of ports 9 have been
positioned on the walls by bending adjacent tubes 11 apart, so that the
ports 9 assume an elongated shape. An air nozzle 12 is positioned between
the tubes 11, which nozzle 12 defines the air port 9. The nozzle 12 is
connected to an air distributing channel 5 surrounding the boiler. The
nozzle 12 is shaped in such a way that it is exactly suitable for the port
9. In this case, the nozzle 12 is, in addition, at the port 9 within a
metal plate box 13, the box 13 being attached to the tube wall of the
boiler. The box 13 is preferably filled with refractory material 20. The
function of the refractory material 20 is to protect the structures 9, 12
and to conduct heat out of the nozzle 12.
From the bed 6, melt is splashed from time to time into the air port 9
(into the inside of the nozzle 12) and to the surroundings thereof in the
furnace 2, so that these structures are exposed to the corroding effect of
the melt and to the detrimental effects of the rapid rise in the
temperature caused by the melt. The temperature in the bed is about
1,000-1,100.degree. C. At this high temperature, in the presence of
corroding substances, the nozzle 12 often becomes completely corroded.
Thereafter, the refractory material 20 in the box 13 outside the nozzle 12
begins to get damaged under the influence of chemical attack. When the
refractory material 20 deteriorates, the damage extends to the box 13,
leading, in the worst case, to the shutting down and the repair of the
entire boiler.
According to the present invention, the corrosion caused by splashing melt
is inhibited by providing a massive protective insert 14 in the air port.
In practice the insert 14 preferably is attached to the bottom of the
nozzle 12 attached to the air port 9. The protective insert 14 is
preferably made of a material which substantially resists the corrosion
caused by the splashing melt. As the combustion air flows into the furnace
2 through the nozzle 12, the protective insert 14 is cooled by air. The
insert 14 is able to store cooling capacity because of the high thermal
mass thereof. Thus, due to the cooling effect of the protective insert 14,
it is possible when melt splashes into the air port 9 to even out and
prevent sudden detrimental rises in the temperature in the air port 9 and
the structures in the vicinity thereof.
The protective insert 14 is preferably made of stainless steel or acid
proof steel, or a like corrosion resistant but heat conductive material.
The protective insert 14 is constantly exposed to very corroding and hot
conditions, so that it will wear away in the course of time. To maintain
the functionality of the protective insert 14 the insert 14 should be
replaced when needed. Therefore, the protective insert 14 is attached to
the nozzle 12 in such a way that it may, if desired, be replaced by a new
one. Attachment between the insert 14 and the nozzle 12 may be effected by
light welding, conventional fasteners, or the like.
The protective insert 14 is preferably disposed in the nozzle 12 in such a
way that it covers the lower part of the air port 9. The protective insert
14 may extend about 100-700 mm, preferably about 150-500 mm, from the
furnace side of the air port 9 towards the air duct (distance h--see FIG.
2). The distance h the insert 14 extends depends on the size of the air
port 9 and the requirements of an air port cleaner, which may be provided
for cleaning of the port 9. The insert 14 may taper--as illustrated in
FIG. 2--so that it has a smaller cross-sectional area more remote from the
box 13 than adjacent the box 13. This tapering minimizes the disturbance
of the air flow from duct 5 through nozzle 12 into the furnace 2.
The size of the protective insert 14 may vary according to the dimensioning
of the air port 9. If the air port 9 is designed for a very heavy load of
black liquor to be burnt in the boiler, but the boiler is in fact run with
a significantly smaller load for a long time, the protective insert 14 is
correspondingly larger. If the height of the air port is 150-200 mm, for
example, the height of the protective insert is typically about 20-50 mm.
A typical volume of the insert 14 is between 40,000 cubic mm-4,000,000
cubic mm, e.g. between about 1-2 million cubic mm. The largest
cross-sectional area of the insert is typically about 10-50%, preferably
about 15-30%, of the cross-sectional area of the air port within the
insert.
FIG. 3 illustrates an air port formed between the bent wall tubes and a
protective insert 14 seen from the side of the furnace 2. The lower
surface 15 of the protective insert 14 is parallel with the corresponding
form of the surface of the air port 9. The upper surface 16 of the insert
14 may be straight (flat as in solid line in FIG. 3) or convexly curved as
indicated at 16' in dotted line in FIG. 3. If surface 16' is curved it
protects the side walls of the air port 9 somewhat better.
The present invention presents a preferable and simple method of protecting
a combustion air port 9 and the structures (e.g. nozzle 12) in the
vicinity thereof against corrosion and heat damage caused by hot melt
splashing. By using a protective insert 14 it is possible to use the
nozzles 12 in air ports 9 longer than in the prior art.
The decrease in the repair shutdowns that ensues according to the invention
results in significant cost savings. In addition, the operational safety
of the boiler is improved, as apparatus damage in the vicinity of the melt
may be prevented. The invention has been described in such a form that it
is applicable especially to boilers burning waste liquor of chemical pulp
mills, but it may also be applied to other combustion apparatus having
corresponding conditions in the vicinity of its air ports.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be
understood that the invention is not to be limited to the disclosed
embodiment, but on the contrary, is intended to cover various
modifications and equivalent arrangements included within the spirit and
scope of the appended claims.
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